Effect of serial extraction alone on crowding: Relationships between toothwidth, arch length, and crowding

In this study, we examined the effect of serial extraction alone on crowdin g. We also investigated the relationships between tooth width, arch length, and irregularity index. Maxillary dental casts from 32 subjects who had un dergone only serial extraction were analyzed at 3 stages: before deciduous canines extraction, after first premolars extraction, and at the end of the observation period. The mean of the irregularity index decreased significa ntly as serial extraction proceeded and further decreased during the observ ation period. In cases where the width of the incisor was more than 2 stand ard deviations above the means for the control subjects, there was a signif icant correlation between tooth width of the lateral incisors and irregular ity index before extraction as well as a significant correlation between th e summation of tooth widths of the central and lateral incisors and irregul arity index at that time. There was a significant negative correlation betw een arch length discrepancy and irregularity index before extraction and al so a significant correlation between arch length discrepancy and correction of the irregularity index from before deciduous canines extraction to afte r first premolars extraction. These results suggest that tooth width and ar ch length discrepancy might preferentially affect the degree of anterior cr owding in cases of severe crowding. There was no aggravation of the average crowding level during the observation period in the present study. The pre sent study quantitatively suggested that serial extraction was useful for t he purpose of correcting crowding in most cases.